The present invention relates generally to electrical distribution equipment, and more particularly to a stab assembly for arc fault circuit breakers that are installed in load centers.
Arc fault circuit breakers are well known, and are used throughout electrical distribution systems to interrupt electrical power supplied to protected loads by electrical busway systems. These circuit breakers function as a manual switch, whereby the breakers disconnect or connect electrical power to the load equipment they are protecting when they are manually opened or closed. The circuit breakers are also equipped with a tripping unit that is capable of automatic interruption and isolation of the protected load from the bus upon the sensing of an electrical fault such as over current and arc-fault conditions. The circuit breaker enclosure, which is generally a molded plastic case, houses the tripping unit. The tripping unit monitors the circuit, and opens the circuit breaker if a fault condition occurs.
Circuit breakers are located in load centers, which contain a power bus and a plurality of cubicles, and which are designed to accept one or more circuit breakers. The cubicles in the load centers function to properly locate and structurally support the circuit breakers. When it is necessary to protect a new load, a circuit breaker is added to an available cubicle in a load center, and conductors are installed from the load to the circuit breaker. Circuit breakers may readily be removed and relocated within the load center as needed to properly supply the protected circuits with electrical current. Because of the diversity of power requirements and associated protection required by different loads, the size and configuration of each circuit breaker may vary.
Although the circuit breaker rating and configuration may vary among the loads connected to the circuit breakers in the load center, each circuit breaker must be configured so as to allow secure insertion into a cubicle in the load center. Proper insertion requires physical contact between the bus and the circuit breaker so that current can pass through the circuit breaker to the load.
Circuit breakers physically mate with stab blades that are electrically connected to the load center. The stab blades conduct the current from the load center to a fixed contact on the circuit breaker. These stab blades are short, stiff conducting metal bars that center the circuit breaker, provide physical support for the circuit breaker, and provide a conducting surface that allows current to flow from the load center to the circuit breaker. The circuit breaker requires a snug fit between the stab blade and the circuit breaker fixed contact in order to function properly. If the fit is not snug, hot spots can occur on the stab blade or fixed contact, and arcing between the stab blade and the fixed contact can result. Hot spots and arcing cause degradation of the circuit breaker, the stab, and/or the load center.
Typical stab assembly designs use a spring plug-in connection to a central stab blade to connect the circuit breaker to the load center. These designs do not lend themselves to be used except in either a right hand (the contact is located to the right of the stab blade), or a left hand configuration (the contact is located to the left of the stab blade). Two separate configurations require at least four separate parts: typically, a left contact, a left spring, a right contact, and a right spring.
Further, the assembly process precludes automated pre-assembly because the stab assembly falls apart unless assembled in the circuit breaker case where the parts are trapped. In addition, the prior art does not fully utilize economies to be gained from using common parts.